/Engine/Source/Runtime/Core/Public/Internationalization/TextLocalizationManager.h
While the engine automatically waits at certain points during initialization, you may find that you need to add your own waits if you cause additional localization data to load post-initialization (eg, because you're using chunked localization targets or are explicitly loading plugins). A good place to add a wait in that case might be at the end of your loading screen, before showing your main menu or game world.
void WaitForAsyncTasks()